| Autor: |
Carder JD; Department of Chemistry, Washington State University, PO Box 644630, Pullman, Washington 99164-4630, United States., Barile B; Department of Bioscience, Biotechnologies and Environment, University of Bari Aldo Moro, Bari 70124, Italy., Shisler KA; Department of Chemistry, Washington State University, PO Box 644630, Pullman, Washington 99164-4630, United States., Pisani F; Department of Bioscience, Biotechnologies and Environment, University of Bari Aldo Moro, Bari 70124, Italy., Frigeri A; Department of Translational Medicine and Neuroscience, University of Bari Aldo Moro, Bari 70124, Italy.; Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, 840 Kennedy Center, Bronx, New York 10461, United States., Hipps KW; Department of Chemistry, Washington State University, PO Box 644630, Pullman, Washington 99164-4630, United States.; Materials Science & Engineering Program, Washington State University, Pullman, Washington 99163-2711, United States., Nicchia GP; Department of Bioscience, Biotechnologies and Environment, University of Bari Aldo Moro, Bari 70124, Italy.; Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, 840 Kennedy Center, Bronx, New York 10461, United States., Brozik JA; Department of Chemistry, Washington State University, PO Box 644630, Pullman, Washington 99164-4630, United States.; Materials Science & Engineering Program, Washington State University, Pullman, Washington 99163-2711, United States. |
| Abstrakt: |
Aquaporin-4 (AQP4) is a water channel protein found primarily in the central nervous system (CNS) that helps to regulate water-ion homeostasis. AQP4 exists in two major isoforms: M1 and M23. While both isoforms have a homotetrameric quaternary structure and are functionally identical when transporting water, the M23 isoform forms large protein aggregates known as orthogonal arrays of particles (OAPs). In contrast, the M1 isoform creates a peripheral layer around the outside of these OAPs, suggesting a thermodynamically stable interaction between the two. Structurally, the M1 isoform has an N-terminal tail that is 22 amino acids longer than the M23 isoform and contains two solvent-accessible cysteines available for S -palmitoylation at cysteine-13 (Cys-13) and cysteine-17 (Cys-17) in the amino acid sequence. Earlier work suggests that the palmitoylation of these cysteines might aid in regulating AQP4 assemblies. This work discusses the thermodynamic driving forces for M1 protein-protein interactions and how the palmitoylation state of M1 affects them. Using temperature-dependent single-particle tracking, the standard state free energies, enthalpies, and entropies were measured for these interactions. Furthermore, we present a binding model based on measured thermodynamics and a structural modeling study. The results of this study demonstrate that the M1 isoform will associate with itself according to the following expressions: 2[AQP4-M1] 4 ↔ [[AQP4-M1] 4 ] 2 when palmitoylated and 3[AQP4-M1] 4 ↔ [AQP4-M1] 4 + [[AQP4-M1] 4 ] 2 ↔ [[AQP4-M1] 4 ] 3 when depalmitoylated. This is primarily due to a conformational change induced by adding the palmitic acid groups at Cys-13 and Cys-17 in the N-terminal tails of the homotetramers. In addition, a statistical mechanical model was developed to estimate the Gibbs free energy, enthalpy, and entropy for forming dimers and trimers. These results were in good agreement with experimental values. |
